1. Technical Field
The present invention relates to a transition metal-noble metal complex oxide catalyst for dehydrogenation, prepared by one-pot synthesis, and to the use thereof.
2. Description of the Related Art
These days, as the production of shale gas containing a large amount of gas such as methane or ethane is drastically increasing, the profitability of a naphtha cracker is decreased and the profitability of an ethane cracker is remarkably increased. Thus, the production of olefins, such as propylene or butylene, as byproducts of the naphtha cracker is greatly reduced. The demand for olefin having a small number of carbon atoms is continuously increasing and the supply of olefin is gradually decreasing. Hence, thorough research is ongoing into propane and butane dehydrogenation processes for directly producing olefin from propane or butane having a small number of carbon atoms.
Examples of a typical catalyst for dehydrogenation of propane and butane may include a Pt—Sn/Al2O3 catalyst (Oleflex process) and a chromia-alumina catalyst (Catofin process), which are already utilized in commercial processes because they have high olefin selectivity and coke stability. However, the Pt—Sn/Al2O3 catalyst is problematic upon repeated catalyst regeneration because the concentration of Sn(0) on the surface of Pt is continuously increased and thus the activity of the catalyst is decreased and Pt sintering may undesirably occur, and hence, an oxychlorination process must be performed during catalyst regeneration in commercial processes. The chromia-alumina catalyst suffers from decreased catalytic activity due to sintering of alumina and movement of Cr3+ upon repeated catalyst regeneration.
With the goal of solving the deactivation of the Pt—Sn/Al2O3 catalyst, the preparation of a Pt—Sn—M/Al2O3-based catalyst by adding the above catalyst with a metal M, such as zinc, lanthanum, lithium, sodium, potassium, or rubidium, has been reported (KR 1,477,413 B1). This catalyst is composed essentially of Pt and Sn, as in conventional cases. In particular, Pt functions as an active component directly participating in dehydrogenation, and the newly added metal M plays an auxiliary role in decreasing the extent of deactivation of Pt and thus the function thereof is limited to dehydrogenation. The Pt—Sn—M/Al2O3-based catalyst is merely a simple extension of the conventional Pt—Sn/Al2O3 catalyst. Furthermore, the Pt—Sn—M/Al2O3-based catalyst requires plurality of metal component impregnation processes, undesirably incurring complicated processing and negating economic benefits.
In order to overcome the limitations of conventional catalysts for the dehydrogenation of propane or butane, a catalyst configured such that Ga and a small amount (0.1 wt %) of Pt are loaded on alumina has been reported in the literature (J. J. H. B. Sattler et al., Angew. Chem., 126:9405, 2014 and US 2013/0178682 A1). This publication proposed gallium oxide as the main active site and reported that Pt aids re-coupling of hydrogen to thus increase reactivity. The corresponding catalyst exhibited early propane conversion of about 46%, but the propane conversion was remarkably decreased to about 30%, corresponding to 60% of the early propane conversion, within 48 hr, and was then maintained at about 30% for 15 days. Based on the results of chemisorption of carbon monoxide (CO), the Pt dispersion was considerably decreased, from 20% to less than 5%, after thermal treatment. Hence, in the dehydrogenation of olefin, it is very difficult to retain the high Pt dispersion under catalyst regeneration conditions of 750° C. and air, and the effective suppression of Pt sintering is regarded as very important in terms of maintaining the early conversion of the catalyst.